The present invention relates to a refrigerating machine, in particular for a domestic refrigerating appliance, as well as to an operating method for a refrigerating machine of said kind.
A refrigerating machine typically comprises a compressor, a condenser and an evaporator which are connected in a refrigerant circuit. Refrigerant compressed by the compressor and heated in the process first flows through a condenser, in which it releases heat to a warm reservoir and condenses in the process, and then through an evaporator, in which it cools down due to expansion to such an extreme extent that it is able to absorb heat from a cold reservoir. The refrigerant evaporated as a result flows back to the compressor.
In most applications of refrigerating machines, in particular in the case of domestic refrigerating appliances, the compressor does not operate continuously, but instead the compressor's operating phases and non-operating phases alternate. Whereas in the operating phases the compressor holds the refrigerant constantly at a high pressure in the condenser and at a low pressure in the evaporator, a pressure equalization takes place between the condenser and evaporator when the compressor is switched off. The drop in pressure in the condenser leads to an adiabatic cooling there, with the result that the thermal energy contained in the refrigerant can no longer be released to the warm reservoir. Conversely there is an increase in pressure in the evaporator, with the result that the temperature of the evaporator—and also that of a space cooled by the evaporator—increases in an undesirable manner.
In order to minimize the energy losses associated with each switching-off of the compressor, it initially appears obvious to make the operating and non-operating phases of the compressor as long as possible. However, long operating and non-operating phases cause extreme temperature fluctuations in the reservoirs. If, for example, the cold reservoir is the storage compartment of a refrigerator, extreme variations in temperature can lead to chilled food products temporarily being inadequately cooled, with the consequence that their storage life is shortened, or to their being damaged due to being supercooled. While no damage to the frozen food is likely in the case of a freezer if the food is cooled down by several degrees below the long-term storage temperature, a temporarily unnecessarily low storage temperature of this kind nonetheless leads to an intensified influx of heat from outside into the storage compartment and is therefore also uneconomical.